PhD Unravelling the physics of hygro-expansion of paper fibres and sheets (V35.2976)

PhD Unravelling the physics of hygro-expansion of paper fibres and sheets

PhD student "Unravelling the physics of hygro-expansion of paper fibres and sheets" (V35.2976) in the section Mechanics of Materials, at the Department of Mechanical Engineering.
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Job description

The mission of the section Mechanics of Materials is to develop and innovate the scientific tools to understand, describe, predict and optimize the mechanical response of industrially relevant materials and products as a function of their underlying microstructure, processing and evolution, through focused and coordinated experimental, theoretical and computational efforts at a wide range of length scales and at the highest scientific level.

Description of project "Unravelling the physics of hygro-expansion of paper fibres and sheets" The processes underlying hygro-expansion at the level of the fibre network of paper are understood only partially and mostly qualitatively. It is clear that cellulose fibres expand transversely upon wetting and this ultimately causes the expansion of the paper sheet. Mutual mechanical constraint between the fibres in the fibre-to-fibre bonds has a major effect on the sheet-level hygro-expansive response, as has been demonstrated by recent micromechanical modelling work. However, quantitative fibre properties which would render such models predictive are lacking, since experiments at the level of single fibres and fibre bonds have proven to be highly challenging. For this reason also, the microstructural origin of the irreversibility in hygroscopic strain is unclear even at a qualitative level. Several possible underlying microstructural processes have been coined in the literature, both at the level of the fibres and the network, but conclusive evidence is lacking for all of them.

We aim to address the above issues by a dedicated, quantitative experimental study of the hygro-expansion of fibres at the micro scale, of fibre networks at the meso scale, and paper sheet at the macro scale; all under different degrees of restraint. To this end, advanced microscopy will be combined with novel digital image correlation techniques to overcome current experimental limitations. Emphasis will be on revealing the main microstructural phenomena underlying irreversible hygroscopic strain and quantifying them. Therefore, the aim of the project is to provide a conclusive and quantitative answer to a long-standing question in paper physics: ‘How does irreversible hygroscopic strain arise?’

Tasks As PhD-student in the project "Unravelling the physics of hygro-expansion of paper fibres and sheets" you will fulfil the following activities:

  • Perform scientific research:
  • Development of an experimental methodology to measure hygro-expansion at the level of individual fibres, based on an advanced digital image correlation algorithm that takes into account knowledge on the mechanics of the system, to extract strain maps with very high accuracy,
  • Preparation of ‘single fibre’ and ‘single bond’ micro-specimens and performing hygro-expansion measurements on these specimens using the smart DIC methodology,
  • Preparation of a handsheet made out of the same pulp and performing hygro-expansion measurements at the sheet scale,
  • Validation of a micro-hygro-mechanical model by comparison with the fibre-scale, network-scale and sheet-scale simulations, which will be done through a close collaboration with the numerical PhD student on a parallel project, who models the hygro-mechanics of fiber networks with computational homogenization of the micro-hygro-mechanical model.
    • Present results on international conferences and publish results in scientific journals.
    • Close collaborate with researchers from project partner Océ.
    • Contribute to the educational program in the department.

Job requirements

Candidate for PhD position should meet the following requirements:

  • MSc in Mechanical Engineering, Applied Physics or other appropriate education with a strong background in experimental micro-mechanics, and solid mechanics theory.
  • Experience with paper sheet fabrication (handling paper pulp and cellulose fibers), paper mechanics, Matlab, and solid mechanics simulations (FEM) are highly recommended,
  • Excellent analytical and communication skills as well as fluency in written and spoken English are essential.

Conditions of employment

We offer:

  • A challenging job at a dynamic and ambitious University, including extensive access to and usage of the Multi-scale laboratory with many advanced mechanical and microscopic characterization techniques (Multi-Scale lab)
  • Support with your personal development and career planning.
  • A full-time employment for 4 years. Gross monthly salaries are in accordance with the Collective Labour Agreement of the Dutch Universities (CAO NU), increasing  from € 2222 per month initially, to € 2840 in the fourth year
  • An attractive package of fringe benefits (including excellent work facilities, end of the year allowance, and sport facilities)

Information and application

More information can be obtained from:

Application Please upload your application with extended curriculum vitae